The invention relates to an agitator assembly for use in an electric blender of the type in which the blender vessel is provided with a large bottom opening through which the drive connection between the motor driven power unit and the blades in the blender vessel must be made. The blender has been a popular and well-accepted domestic appliance for more than twenty-five (25) years. It is characterized by being powered by a powerful motor which drives blades which chop and mix the contents of the blender vessel. Although most blenders are adapted to operate at a range of different speeds, the maximum speed is usually on the order of 18,000 to 20,000 revolutions per minute under no load and 5,000 to 11,000 revolutions per minute under load.
This requirement that the blades rotate at such high speeds necessitates the use of a strong well-aligned drive connection between the motor and the blade assembly. Because of the substantial amount of power and speed involved, any significant misalignments in the driving connection can cause serious vibration and wear. The problem is further complicated by the fact that the bearings for the blade supporting shaft must maintain their leakproof condition since even though the blender vessel is sometimes filled with dry foods, it is more often than not utilized in connection with liquids.
Although some of the prior art blenders utilize cup-shaped blender vessels in which the blades and their supporting shaft are permanently mounted in the bottom of the vessel, the more popular approach from the consumer's standpoint is one in which the agitator assembly and the bottom wall of the vessel which supports the assembly are removable for cleaning purposes. The latter type of approach presents some sealing problems in that the separable bottom wall must normally seal against the periphery of an opening in a glass vessel. To facilitate sealing against the molded walls of the glass vessel, it is known to use a flexible diaphragm member which in combination with the sealing gasket is clamped against the bottom wall of the vessel. The flexibility of the diagram can accommodate variations in the dimensions of the glass vessel.
In the prior art blenders utilizing such diaphragm bottoms, it has been known to form a flange on the diaphragm within which a pair of spaced axially aligned bearings would be mounted. A drive shaft would then be utilized which would mount the blade assembly at the upper end within the vessel and have a splined opening in the lower end thereof to receive the output shaft of the motor drive unit. This arrangement provided the detachable drive connection between the motor and the blades permitting the blender vessel to be separated from the power unit so it may be washed more readily.
The one-piece shaft and the spaced bearings which supported it, tended to be high in manufacturing cost and difficult to manufacture properly. The one-piece shaft was of reduced diameter at its upper end where it was journaled in the upper bearing and was of substantially greater diameter at its lower end where it had a machined cavity to receive the output drive shaft. This shape resulted in a part that was very expensive to manufacture, requiring a considerable amount of machining. In addition, because of the fact that two spaced bearings were mounted in a drawn flange in the diaphragm, it was difficult to achieve accurate alignment of the bearings so that the one-piece shaft would be properly journaled therein.
Another problem which increased the cost of the prior art agitator assembly was the requirement that the parts be corrosion resistant. This required the use of stainless steel material. Typically, a piece of 1/2 inch stainless steel bar stock would be used to turn down and machine the upper portion of the shaft, while drilling, undercutting and broaching the lower end of the shaft was required for the splined drive connection. All of these operations were particularly expensive considering the necessity that stainless steel be used. It would be desirable, therefore, to provide an agitator assembly which would be easier and less expensive to manufacture than the prior art devices.